The present invention relates to an arrangement for covering over the expansion joint of a bridge or the like and comprising parallel support bars running athwart the roadway of the bridge, transverse beams each swivelingly and slidingly supported at its two ends on the different sides of the expansion joint so as to span the joint at an angle to the direction of the roadway for supporting the said bars by way of a anti-friction bearing means and running through openings in the bars or in lower members attached thereto. In this respect the bearing means may be in the form of swivel-slide, elastically yielding bearings that each have at least one bearing body and which are not able to be turned in relation to the transverse beams but, slidingly joined thereto, are swivelingly joined to the bars.
In the prior art one form of cover designed on these lines for an expansion joint has been proposed in the German Pat. No. 2,746,490. In this design the bearing bodies were generally in the form of circular disks, each having a groove for one of the transverse beams to slide in relatively. There were projections next to the groove on the bars to function as guides for the sliding motion of the transverse beam. Simultaneously they functioned to transmit horizontal forces from the bar to the transverse beam.
This system for the transmission of horizontal forces from the bar to the transverse beam was beset with a number of serious shortcomings in the prior art expansion joint cover. Inasmuch as the transverse beams were placed at a slant in relation to the bars, forces were transmitted to the transverse beams which were made up both of a component in the lengthways direction of the beams as well as a force component in the transverse direction of the beam. The lengthways forces caused a placement of the bearing bodies in relation to the transverse beams, if they are in excess of the friction forces acting in the opposite direction, whereas the transverse forces were passed on by the projections on the side of the grooves to the side walls of the transverse beams. The projections placed round the transverse beams had the form of sections of a circle because of the round form of the bearing bodies, only a small area being available for the transmission of transverse forces to the transverse beams, seeing that for effective transmission of forces it is necessary for such projections to have a substantial wall thickness, such thickness however only being present in the middle part of the projections. The outcome of this is that because of the transmission of transverse forces the projections of the bearing bodies were acted upon by very large loads that were are likely to be responsible for rapid wear of the bearing bodies.
Braking or acceleration forces and the eccentric line of action of the vertical wheel load on the bars produce a tilting moment that tends to lift the bar from the bearings placed on the transverse beams. This tilting moment was to be taken up in the prior art joint cover system by using a substantial vertical pre-loading force to keep the upper and lower bearing bodies in proper engagement with the transverse beams. For its part however this large pre-loading force resulted in a large amount of friction between the bearing bodies and the transverse beams so that the slipping clutch effect, desired between the bearing bodies and the transverse beams in order to stop overloading of the bar because of braking forces only came into being when the braking forces were very large. If in the course of time there is a decrease in the pre-loading effect because of relaxation of the bearing bodies, there is then a danger that the bar will suddenly come clear of the bearing bodies when a tilting moment takes effect. This will then make such a bearing body unserviceable within a short period of time.